The city of Mosul was declared as "liberated" from Islamic State two weeks ago, but a very different and challenging fight is looming 231 miles to Mosul's west in the Syrian city of Raqqa.

Mosul's liberation from Islamic State came at great cost both to civilians and to members of the Iraqi Security Forces who fought an urban war on a scale which hasn't been seen since World War Two.

The ten months of continuous battle for Mosul lasted longer than the Battle of Stalingrad, and the ISF suffered close to 1,000 killed and more than 6,000 wounded.

The cost of civilian lives is also believed to be very high, though the exact numbers are still to be determined.

Now, attention is turning to the battle to liberate Raqqa from IS control and the difference between the old campaign in Iraq and the new fight in Syria is visible from the start.

Video:Iraqis have celebrated the liberation of Mosul

A combined force of 105,000 fought to liberate Mosul, including 60,000 from the Iraqi Security Forces (ISF) and an assortment of Iraq's Popular Mobilisation Force militias which received extensive training by coalition partners over an 18 month period.

The lead units which spearheaded the Mosul operation - the 10,000 strong Iraqi Counter Terrorist Service forces and the 1,200 strong Emergency Response Division - were trained in urban warfare along the lines of US Army Ranger Battalions and went about a number of tactical changes during their nine months of fighting.

In Syria, the men and women of the Syrian Democratic Forces (SDF), including the mostly Kurdish People's Protection Units (YPG) do not have the luxury of such numbers.

The YPG/SDF forces are about 50,000 strong and have received basic tactical training - marksmanship skills, fire manoeuvre, basic urban warfare tactics and first aid training have been jammed into two week periods when and where possible.

Image:A Kurdish fighter from the People's Protection Units (YPG) adjusts a gun on top of an armored vehicle in Raqqa

For them, the training happens more on the job, and their spearhead forces that are leading the assault are much smaller in comparison to the ISF's lead units.

In terms of troop numbers, while the ISF were stretched, the Popular Mobilisation Force militias, alongside the Peshmerga, regular army, and Police units provided the necessary support in holding ground taken by lead units.

From the onset the YPG/SDF are stretched across multiple battlefronts.

But across the Tigris River, back in Iraqi Kurdistan, the Kurdish Regional Government's Rojava Peshmerga force of exiled Syrian Kurds, numbering between 4,000 and 6,000 men and women, sits idle.

Trained by the "Zeravani force" the Rojava Peshmerga would add strength to the Raqqa offensive, especially as casualties mount - but Kurdish politics prevents them from joining the fight because the Rojava Peshmerga and the YPG are supported by different political parties. It's not so clear cut even with the Kurds.

Image:Kurdish fighters from the People's Protection Units (YPG) run across a street in Raqqa

There is also a significant difference in armaments between those forces opposing IS in Mosul and Raqqa.

After the ISF's earlier setbacks in 2014, the force was heavily rearmed with the latest American weapons, including .50 Calibre HMG, automatic 40mm grenade launchers, anti-tank missiles, mortars and American-made M1 Abrams tanks.

The ISF also had reliable and accurate fire support, with unlimited ammunition, and its troops rode in heavily armoured Humvees.

These troops had their own Close Air Support (CAS) in the form of the Iraqi Army Air Corp attack helicopters and were supported by coalition jets and UAV drones for continuous intelligence, surveillance and reconnaissance, as well as missile strikes.

These eventually proved effective against Islamic State's SVBIEDs (Suicide Vehicle-Borne Improvised Explosive Devices, which consisted of everything from modified civilian cars to trucks and bulldozers).

From October through to June, the coalition conducted 315 airstrikes against IS SVBIEDs. While the total number of SVBIED attacks is unknown, on average there were five per day.

Video:Heavy gunfire as Syrian forces take on IS

Such luxuries are not available for the YPG/SDF, who are courageous fighters but lack the modern weapons that the Iraqi forces were issued following their early troubles in 2014.

Their tanks are antiquated Russian types - T55s and T64s - and most of their small arms and heavy weapons are of Russian configuration; prone to jamming and not as accurate as modern US weapons as used by Iraqi forces.

The YPG/SDF also ride on the back of pick-up trucks or move by foot, in stark contrast to the Humvees in which the ISF manoeuvred. Armoured fighting vehicles are very limited and individual body armour for troops is non-existent.

Arming and retraining the YPG/SDF is a delicate issue. It could extensively expand the geopolitical mess that encompasses this region.

Turkey is watching this closely and robustly challenging the US on its actions but the Americans have followed through with their plan of arming their allies to defeat IS in Raqqa. It's a calculated risk.

Image:Smoke billows after an air strike by Iraqi forces towards Islamic State militants in the Old City of Mosul

Comparing the two cities as an objective is difficult.

Mosul is a very large ethnically diverse city with a pre-conflict population of 1.5 million people.

The east was cleared in three months. The west side took more than six months. Tactical changes were made to reduce attrition rates and counter IS tactics.

Also, concern for taking Mosul with minimum damage to civilians and infrastructure was very much in mind but that was gradually lost in the last few weeks.

Raqqa is probably more comparable to being slightly smaller than West Mosul. It was once populated by 220,000 people, which has dramatically reduced over the last two years under IS.

Image:Mosul's Old City has been severely damaged in the fighting

In Mosul, the Coalition was very active in supporting the ISF. In Raqqa, the men of the Combined Joint Task Force - Operation Inherent Resolve are very visible on the frontline calling in airstrikes and advising YPG/SDF ground forces.

The CJTF-OIR numbers are growing, US artillery is in place and various other nations have their SF Teams in forward positions. They will be critical in directing the air support that will assist the YPG/SDF to attack on multiple axes.

55km north of Raqqa in the small town of Ain Issa, Ferass Fahad of the Raqqa Civil Council stands on the office's steps messaging people still trapped in Raqqa. Wi-Fi and cellular connection in the city is very sporadic but Ferass manages to get through.

He informs them of the safe routes out of the war torn city, picks up the odd bit of intelligence and maintains confidence that this will soon be over so then he can return to his home town.

The YPG/SDF and its coalition partners will succeed in liberating Raqqa, once liberated it's only the end of one more chapter as the Middle East is reshaped. The question is what will regional powers and partners want next.